In recent years, IP telephone systems, which bidirectionally exchange image and audio data as packet data in realtime via Internet Protocol (IP) networks such as a LAN and the Internet, have prevailed. In this IP telephone system, for example, an IP telephone server is equipped for each company or individual user, and IP telephone stations can be registered for each IP telephone server. In such IP telephone system, not only inter-extension communications and outside outgoing/incoming call can be made but also those between IP telephone servers can be made via the IP network.
When each company or user purchases and uses an IP telephone server, an IP telephone server including functions required at that time is selected. However, after the beginning of use, functions of the IP telephone server are required to be added and unnecessary functions are required to be reduced according to an increase in personnel, a change in business content, and the like. Also, for each company or user, the number of IP telephone servers is required to be increased or decreased.
However, immediate addition/reduction of functions or expansion/reduction of IP telephone servers imposes a heavy load on each company or user side.